Typically, broadband wireless communication standards beyond 3G, e.g. 3GPP LTE, IEEE 802.20, and IEEE 802.16e-2005 (mobile WiMAX) use uplink (UL) grant scheduling to exploit user diversity, to offer Quality of Service (QoS) support, and/or to provide good spectral efficiency. However UL grant scheduling generally is different from downlink (DL) scheduling in several aspects. First, the UL scheduler generally does not have the detailed buffer information ready as the DL scheduler does. Each mobile station (MS) therefore generally needs to update its buffer level at the base station (BS) for efficient scheduling.
Second, it is often the case that the UL buffer level update does not have the same detailed granularity as DL buffer information. The DL scheduler typically has all the information for each connection identifier (CID). However, for UL scheduling, maintaining such detailed buffer information would result in an increased load for the UL signaling channel and thus incur significant overhead.
Third, it is typical to arrange all UL grant request in a common contention channel shared by all users such that signaling overhead is incurred only when necessary, i.e., when a MS has data to send in a UL frame.
Furthermore, the UL contention-based access and resource allocation mechanisms in IEEE 802.16e-2005 based systems (mobile WiMAX) includes random access and bandwidth request stages that generally result in additional access latency. In the current IEEE 802.16e-2005 standard, the UL grant request happens first in the contention-based ranging channel. Additionally, upon a successful contention, BS allocates grant for a bandwidth request and then a bandwidth request is issued by MS to the BS. The contention-based UL bandwidth request may take four or possibly more frames, depending on the implementation and transceiver switching time. Thus there can be delay and potentially a large overhead associated with grant requests and bandwidth request, especially with respect to small grant requests.